In a so-called indirect AC power converting apparatus, a large-size capacitor is provided at a so-called DC link between a converter and an inverter. This capacitor has a function to smooth a voltage ripple caused by the commercial frequency. This technique is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-224393 (1997). According to this document, an inverter section for a compressor and an inverter section for a fan are connected in parallel with respect to a smoothing capacitor, to thereby share a power source between both of the inverter sections. In this technique, a DC voltage is shared between both of the inverters, and therefore a control of the fan is corrected in accordance with the DC voltage which varies in accordance with a load of the compressor.
On the other hand, in a direct AC power converting apparatus, a large-size capacitor or reactor is not required. Therefore, in this converting apparatus, downsizing can be expected, and in recent years, there has been an increasing interest in it as a next-generation power converting apparatus. For example, Japanese Patent Application Laid-Open No. 2007-312589 introduces a technique in which one inverter is connected to one converter, and a commutation is caused in the converter when the inverter is operated based on a zero vector and a so-called zero-current state is established (hereinafter, sometimes represented simply as “a commutation in a converter at a zero current”). There is also introduced a technique by which a carrier can be shared between the converter and the inverter.
As for the direct AC power converting apparatus, a technique has also been proposed in which an operation is performed with a plurality of inverters being connected with respect to one converter for the purpose of driving a plurality of loads. This technique is disclosed in, for example, Kato and Ito, “Improvement of Waveform for a Boost type AC/DC/AC Direct Converter”, Institute of Electrical Engineers of Japan, national convention 2007 Mar. 15-17, Part 4, 4-098. In this document, a DC/DC converter and a voltage-source inverter are connect in parallel with each other. A current-source rectifier can be recognized as a converter, and the DC/DC converter can be recognized as an inverter. According to the technique shown in this document, in order to cause a commutation in the current-source rectifier at a so-called zero current, a plurality of inverters are controlled by a pulse-width modulation by a single carrier synchronized with a carrier based on which the current-source rectifier is operated.
Japanese Patent Application Laid-Open No. 9-182458 (1997) introduces a technique in which switching for generating a current-source pulse-width control pattern is controlled by using a result of comparison between a carrier and a command value of a phase current which is dual to a phase voltage.
Japanese Patent Application Laid-Open No. 2004-266972 discloses a technique in which inclination is different between a carrier used for a pulse-width modulation of a converter and a carrier used for a pulse-width modulation of an inverter.